Beadle's Static Blast

You harness the power of electricity to both harm and hinder your foes, By sending forth a bolt of lightning you interrupt the natural flow of a persons biochemistry allowing your further assault to be more effective.

As an action you may choose one creature within range, make a spell attack roll. On a hit the creature takes 2d8 Lightning damage and must make a Constitution saving throw or gain vulnerability to Lightning Damage until the end of your next turn. 

When you cast this spell at 2nd level or higher, the damage increases by 1d8 for each slot level above 1st.